1.4. GHC version numbering policy

As of GHC version 6.8, we have adopted the following policy
for numbering GHC versions:

Stable Releases

Stable branches are numbered x.y, where
y is even.
Releases on the stable branch x.y are numbered x.y.z, where
z (>= 1) is the patchlevel number.
Patchlevels are bug-fix releases only, and never
change the programmer interface to any system-supplied code.
However, if you install a new patchlevel over an old one you
will need to recompile any code that was compiled against the
old libraries.

Stable snapshot releases are named
x.y.z.YYYYMMDD.
where YYYYMMDD is the date of the sources
from which the snapshot was built, and x.y.z+1 is the next release to be made on that branch.
For example, 6.8.1.20040225 would be a
snapshot of the 6.8 branch during the development
of 6.8.2.

The value of __GLASGOW_HASKELL__
for a snapshot release is the integer
xyy. You should never write any
conditional code which tests for this value, however: since
interfaces change on a day-to-day basis, and we don't have
finer granularity in the values of
__GLASGOW_HASKELL__, you should only
conditionally compile using predicates which test whether
__GLASGOW_HASKELL__ is equal to, later
than, or earlier than a given major release.

Unstable snapshot releases are named
x.y.YYYYMMDD.
where YYYYMMDD is the date of the sources
from which the snapshot was built.
For example, 6.7.20040225 would be a
snapshot of the HEAD before the creation of the
6.8 branch.

The value of __GLASGOW_HASKELL__
for a snapshot release is the integer
xyy. You should never write any
conditional code which tests for this value, however: since
interfaces change on a day-to-day basis, and we don't have
finer granularity in the values of
__GLASGOW_HASKELL__, you should only
conditionally compile using predicates which test whether
__GLASGOW_HASKELL__ is equal to, later
than, or earlier than a given major release.